Consequences of Running (Too) Shallow

Consequences of Running (Too) Shallow
The bearing carrier lock screw should be aligned with the skeg. Note that it has been twisted clockwise, slightly out of alignment. This is evidence that the prop shaft has been subjected to excessive torque from the propeller and a seal failure is likely.

There seems to be an increasing tendency to accomplish ever-shallower takeoffs, and also to plane at the lowest possible speed in shallow water. Nothing new about shallow water boating; we own Flats Cat Boat Company. The Flats Cat can run shallower than many flats boats, and as a cat hull it is exceptionally stable. The difference is the way our boat planes and where the motor sits between the sponsons. It’s about finesse, not horsepower.

The reason for this article is to discuss customized props we see folks using that can be detrimental to the lower unit, not to mention the damage that can be done to seagrass beds.  

We frequently see heavily cupped custom three-blade props, and recently a twin-prop setup where two props are welded into a single unit. Others have special tips added to the blades to grab more water.

Many lower units, especially Mercury's higher-horsepower models, are not engineered to withstand the amount of additional torque generated by these – not to mention that no lower unit is designed to be used as a plow. The bearing carrier can spin out of position causing seal damage that allows water to enter the gearcase. We also see prop shafts twisted and snapped from unusual torque loads.

There are many excellent propellers available that can do the job without risking damage to the lower unit.

Seagrass is the foundation of the marine food chain. Save the seagrass and save yourself a few bucks in the process. Be mindful of water depth when entering shallow water!   

Stop in any time for a discussion of “proper” propping.

Chris Mapp

Coastal Bend Marine – 361-983-4841 – [email protected]